Broach and broach machine: stretching of metal
The broach is a tool, by means of which processing of metal by stretching is carried out (one of the most common technological operations for metal cutting). This technology is used for details, used in many industries.
The working surface of broaches can have a different profile depending on purpose and type of the tool
What is needed for stretching
Such a technological operation, as a broach, is considered one of the most effective ways of processing metals by cutting. To perform it, you need a long machine and a special tool, the use of which gives a surface with a roughness of order 0,32 μm and the accuracy of the geometric parameters of the corresponding 6 quality.
Tool, by means of which the long metal-cutting processing is carried out, consisting of many teeth. Each of them is higher than the other, if you measure their height in the plane, perpendicular to the direction, in which the main cutting movement is carried out. Equipping the broach with many cutting blades and placing them in a certain position allows you to use only one such tool to, to remove all the necessary amount of chips in the process of roughing the surface, and when calibrating it.
Most long machines are set up to process the same type of parts
Using long machines, as well as a specialized tool, can be processed as external, and internal surfaces of products of various configurations. No feed movement is used when pulling: all processing is carried out by carrying out a broach of the main movement, which can be rotational or translational. The tool for stitching holes works on a similar principle. Despite all the similarities between these technological operations, the fundamental difference between them is, that the firmware tool works on compression, and broaching - stretching.
The video below shows the process of processing the inner surface of the pipe by drawing.
Drawing, if you compare it with other methods of metal cutting, has a whole list of advantages, which should include:
- the ability to reduce equipment operating costs, used;
- high wear resistance of a broach;
- high minute feed rate due to that, that the treatment is performed by several cutting teeth;
- the ability to work on long machines, even specialists with a low level of training;
- removing the allowance from the surface at a high relative speed (this means high processing productivity);
- the ability to eliminate any kind of defect of the treated surface;
- high accuracy of processing of metal products.
Schemes of different types of drawing holes and surfaces
Tool, which are equipped with long machines, is made mainly of high-speed steels with a medium level of alloying, are quite expensive. For this reason, its use is recommended for production, producing their products in large and mass series.
Meanwhile, the use of broaching machines and broaching can be used in small-scale and single production of metal products, if their geometric parameters are standardized. Do not do without such a technological operation in those cases, when it is the only possible or best way of processing.
Varieties and design of broaches
Drafts are classified according to a number of parameters. There are the following types of broaches:
- with cutting part, made of high-speed, tool steel or hard alloy;
- solid or prefabricated - depending on the design;
- single - or multi-pass - depending, how many broaches are contained in one working set;
- work in stages, profile or progressive methods - depending on, how the allowance is removed from the surface of the part;
- with straight and inclined or helical and annular arrangement of cutting blades on the working part.
Significant elements of a round broach
Different types of broaches are distinguished by their main purpose, moreover, such a classification can be called one of the most important. So, depending on this parameter distinguish broaches for external and internal surfaces. With the help of a tool, designed to perform external work, it is possible to carry out processing of surfaces of various configuration (gears, Christmas tree type profiles, watch out, including T-shaped, cylindrical shafts, grooves of different shapes, including "swallow's tail", splined shafts, etc.).
Broaches of various profile can be processed by a broach
Hole drawing is a more common technological operation, than stretching of external surfaces. Using a broaching machine and broaching, it is possible to process internal surfaces of the following types:
- keyways;
- screw-type grooves;
- round holes (broaches for round openings);
- holes with different number of faces (face broaches);
- holes with slots (broaches).
Slotted broach for processing of openings
Though, that different types of broaches are used for finishing of internal surfaces, the design of these tools is almost identical and includes several components.
The front part
This is a guiding element. Before processing, the part is fixed on the front of the tool, which then smoothly transmits the treated surface to the cutting edges of the broach. The nominal cross section of the front of the tool and the size of the machined holes must match, and the choice of the degree of landing is made taking into account the required gap between the broach and the walls of the hole.
Shank
With this element, the broach is fixed in the chuck of the equipment used. For broaches as round, and flat type shank sizes are strictly stipulated by the provisions of relevant regulations (Guests 4043-70 and 4044-70).
Standard slotted shank
Cutting part
This element of a broach consists of set of teeth and is responsible for removal of the necessary allowance from the processed surface.. Geometric parameters of cutting teeth of a broach, starting from its front part and ending with the back, gradually changing. So, the front tooth has the shape and size of the hole, to be processed, and the rear cutting element differs in geometric parameters, the corresponding characteristics of the already finished hole. Due to that, that the height of the teeth of the broach gradually increases to its rear, there is no feed movement when processing, while the allowance from the treated surface is effectively removed.
The main elements of the cutting part of the keyway
Supporting head
Long and heavy broaches are equipped with this element for that, to provide their support with a lunette.
Rear guide part
This part of the broach is necessary for that, that the processed detail did not warp at an exit from its aperture of the last cutting tooth.
Calibration part
This element is characterized by fewer teeth, than the cutting part of the broach. Shape and size of teeth, located on the calibration part, completely identical to similar parameters of the finished hole.
In order to detect errors, the parameters of broaches are periodically monitored. The photo shows a check of the front and rear corners of the keyway
Types of slotted broaches and their scope
Slotted broach, as mentioned above, it is applied to processing of internal surfaces, on which there are slotted elements. Such tools depending on the number and type of cutters, which they are equipped with, can be:
- involute;
- pointed;
- 6-slotted;
- 8-slotted;
- 10-slotted.
The broach for slotted openings of TsL-2408-4333-8X42X46 is made of P6M5 steel
Spline broaching depending on its type can be carried out on one of the following regulatory documents:
- with involute type profile: 50038-92 - two-pass combined; 50035-92, 28050-89 - the usual combined type; 25158-82, 25159-82 - for processing of an aperture by section 15-90 mm; 25157-82 - for processing of openings in diameter 12-14 mm; 25160-82 - for processing of openings by section 45-90 mm;
- with a rectangular profile: 25971-83, 25972-83 - for processing of octagonal openings; 25969-83, 25970-83 - for processing of six-slot openings; 24822-81, 24823-81 - for ten-slot openings;
- with a screw shank: R 50035-92, 50036-92, 50037-92, 28048-89, 28049-89 etc.
In some cases, when it is not possible to choose a standard tool, production of broaches can be carried out according to specially developed design documentation.
Using slotted broaches, you can effectively perform such technological operations:
- cutting of keyways and slots;
- processing of barrels of rifled weapons;
- calibration of internal holes of different types;
- production of turbine elements for aircraft engines;
- stretching of external surfaces, differing in a difficult configuration.
Drawing equipment
Drawing machines are divided into different types according to a number of parameters. Such parameters, in particular, is:
- purpose - to perform treatment of external or internal surfaces;
- degree of universality - general and specialized machines;
- direction, in which the stretched element moves (labor movement), horizontally extended machines vertically extended;
- type of work movement performed - with circular motion, with the movement of the broach or workpiece;
- the number of carriages installed on the machine - one - or multi-carriage;
- the number of positions occupied by the working mechanism of the machine - one - and multi-position (with a rotating desktop);
- level of automation - with CNC and without.
The main parts of long machines
The most common types of such equipment are:
- horizontal-extended universal machine, which is used to treat internal surfaces;
- vertical type machines, which can be used both for external, and for internal surfaces;
- CNC equipment, which can be like a horizontally extended machine, and vertically long (on such equipment the processes of installation and removal of the processed preparations are automated, as well as replacement of the working tool).
Choosing equipment to perform stretching, specialists focus on two main parameters of such machines: developing traction, the value of which may be in the range 50-1000 kN, and the length of the broach, which can be selected in the range 1000-2000 mm
